Aging calibration for temperature sensor

ABSTRACT

A thermal sensor with non-ideal coefficient elimination is shown. The thermal sensor has a bandgap circuit, a dual-phase voltage-to-frequency converter, and a frequency meter. The bandgap circuit outputs a temperature-dependent voltage. The dual-phase voltage-to-frequency converter is coupled to the bandgap circuit in the normal phase to perform a voltage-to-frequency conversion based on the temperature-dependent voltage, and is disconnected from the bandgap circuit in the coefficient capturing phase to perform the voltage-to-frequency conversion based on the supply voltage. The frequency meter is coupled to the dual-phase voltage-to-frequency converter to calculate the temperature-dependent frequency corresponding to the normal phase of the dual-phase voltage-to-frequency converter. The frequency meter also calculates the temperature-independent frequency corresponding to the coefficient capturing phase of the dual-phase voltage-to-frequency converter. The temperature-dependent frequency and the temperature-independent frequency are provided for temperature evaluation with non-ideal coefficient elimination.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Applications No.62/857,932 filed on Jun. 6, 2019 and No. 62/860,299 filed on Jun. 12,2019, the entirety of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a chip with a thermal sensor design.

Description of the Related Art

In electronic devices, e.g., modern mobile devices using a fastapplication processor (AP), the highest operating speed is generallylimited by thermal issues. Hence accurate temperature sensing isessential for maximizing the operating speed of an electronic device.Typically, a thermal sensor is placed in a chip. Aging of the resistorsand capacitors of the thermal sensor may deteriorate the accuracy oftemperature sensing. Or, packaging stress may also change the resistorsand capacitors used in the thermal sensor and thereby affect thetemperature sensing.

Calibration for a thermal sensor is required.

BRIEF SUMMARY OF THE INVENTION

One of the objectives of the claimed invention is to provide a thermalsensor calibration technique.

A thermal sensor in accordance with an exemplary embodiment of thepresent invention has a bandgap circuit, a dual-phasevoltage-to-frequency converter, and a frequency meter. The bandgapcircuit outputs a temperature-dependent voltage. The dual-phasevoltage-to-frequency converter is coupled to the bandgap circuit in thenormal phase to perform a voltage-to-frequency conversion based on thetemperature-dependent voltage. The dual-phase voltage-to-frequencyconverter is disconnected from the bandgap circuit in the coefficientcapturing phase to perform the voltage-to-frequency conversion based onthe supply voltage. The frequency meter is coupled to the dual-phasevoltage-to-frequency converter to calculate a temperature-dependentfrequency corresponding to the normal phase of the dual-phasevoltage-to-frequency converter and a temperature-independent frequencycorresponding to the coefficient capturing phase of the dual-phasevoltage-to-frequency converter. The temperature-dependent frequency andthe temperature-independent frequency are provided for temperatureevaluation with non-ideal coefficient elimination.

In an exemplary embodiment, the thermal sensor further has a charge pumpcircuit pumping the supply voltage to a higher level for operations ofthe bandgap circuit. The bandgap circuit further generates atemperature-independent reference voltage to be coupled to thedual-phase voltage-to-frequency converter with the temperature-dependentvoltage.

In an exemplary embodiment, the dual-phase voltage-to-frequencyconverter comprises a switched-capacitor integrator loop. In the normalphase, the temperature-dependent voltage and the temperature-independentreference voltage are coupled to the switched-capacitor integrator loopand the switched-capacitor integrator loop generates an oscillationsignal oscillating at the temperature-dependent frequency. In thecoefficient capturing phase, a first direct-current voltage and a seconddirect-current voltage derived from the supply voltage are coupled tothe switched-capacitor integrator loop and thereby the oscillationsignal generated by the switched-capacitor integrator loop oscillates atthe temperature-independent frequency.

In an exemplary embodiment, the switched-capacitor integrator loop hasan integrator, a switched-capacitor resistor coupled to the integratorthrough an input terminal of the integrator, a voltage controlledoscillator, and a divider. The switched-capacitor resistor receives thetemperature-dependent voltage when the temperature-independent referencevoltage is coupled to a reference terminal of the integrator, andreceives the first direct-current voltage when the second direct-currentvoltage is coupled to the reference terminal of the integrator. Thevoltage controlled oscillator generates the oscillation signal accordingto an output voltage of the integrator. The divider operates theswitched-capacitor resistor to mimic a resistor based on the oscillationsignal.

In an exemplary embodiment, the switched-capacitor resistor has a firstswitch and a second switch controlled by an output signal and aninversed output signal of the divider, respectively, and a capacitor.The capacitor has a first terminal for receiving thetemperature-dependent voltage or the first direct-current voltage and asecond terminal coupled to the input terminal of the integrator throughthe second switch. The first switch is coupled between the firstterminal and the second terminal of the capacitor.

The temperature-dependent frequency and the temperature-independentfrequency may both involve information about the capacitor of theswitched-capacitor resistor that is affected by the aging effect orpackaging stress. By combining the temperature-dependent frequency andthe temperature-independent frequency, non-ideal coefficients due to thecapacitor of the switched-capacitor resistor are eliminated andtemperature data for evaluation of a temperature value is evaluated.

In another exemplary embodiment, a chip comprising the aforementionedthermal sensor and a processor is shown. The processor evaluatestemperature data based on a temperature-dependent period derived fromthe temperature-dependent frequency and a temperature-independent periodderived from the temperature-independent frequency, and evaluates atemperature value based on the temperature data. When evaluating thetemperature data, the processor eliminates non-ideal coefficients of thetemperature-dependent period by the temperature-independent period.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 depicts a chip 100 with a thermal sensor 102 in accordance withan exemplary embodiment of the present invention;

FIG. 2 depicts the details of the dual-phase voltage-to-frequencyconverter 108 in accordance with an exemplary embodiment of the presentinvention; and

FIG. 3 is a flowchart depicting a thermal sensing procedure of thethermal sensor 102 in accordance with an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain terms are used throughout the following description and claims,which refer to particular components. As one skilled in the art willappreciate, electronic equipment manufacturers may refer to a componentby different names. This document does not intend to distinguish betweencomponents that differ in name but not in function. In the followingdescription and in the claims, the terms “include” and “comprise” areused in an open-ended fashion, and thus should be interpreted to mean“include, but not limited to . . . ”. Also, the term “couple” isintended to mean either an indirect or direct electrical connection.Accordingly, if one device is coupled to another device, that connectionmay be through a direct electrical connection, or through an indirectelectrical connection via other devices and connections.

FIG. 1 depicts a chip 100 with a thermal sensor 102 in accordance withan exemplary embodiment of the present invention.

Instead of using a resistor or an ETF (electrothermal filter), thethermal sensor 102 is in a transistor-based design, which is more robustfor mass production and its temperature coefficient model is moreaccurate in the design phase. The thermal sensor 102 has a charge pumpcircuit 104, a bandgap circuit 106, a dual-phase voltage-to-frequencyconverter 108, and a frequency meter 110. A supply voltage VDD (e.g.,around 0.5V, like 0.568V) is pumped to a higher level CPV (e.g., around1.2V) for operations of the bandgap circuit 106 and thereby provides agreater headroom for the bandgap circuit 106.

The bandgap circuit 106 includes transistors whose junction forward-biasvoltage VBE varies with the junction temperature. The bandgap circuit106 outputs a temperature-independent reference voltage VREF as well asa temperature-dependent voltage VBE/2. In the normal phase, thedual-phase voltage-to-frequency converter 108 performs avoltage-to-frequency conversion based on the temperature-dependentvoltage VBE/2 and the temperature-independent reference voltage VREF. Anoscillation signal Sosc oscillating at a temperature-dependent frequencyF1 is generated.

In addition to the normal phase, a coefficient capturing phase isspecifically provided in the present invention. In the coefficientcapturing phase, the dual-phase voltage-to-frequency converter 108 isdisconnected from the bandgap circuit 106. Instead, the dual-phasevoltage-to-frequency converter 108 performs the voltage-to-frequencyconversion based on the supply voltage (e.g., VDD and VDD/2). Thegenerated oscillation signal Sosc is changed to oscillate at atemperature-independent frequency F1_Coeff. The temperature-independentfrequency F1_Coeff is used in non-ideal coefficient elimination.

The temperature-dependent frequency F1 and the temperature-independentfrequency F1_Coeff are calculated by the frequency meter 110. Thefrequency meter 110 may be a digital back-end of the transistor-basedthermal sensor 102, and is coupled to a processor 112 of the chip 100.The processor 112 may derive a temperature-dependent period Period_1from the temperature-dependent frequency F1, and atemperature-independent period Period_2 from the temperature-independentfrequency F1_Coeff. The non-ideal coefficients of thetemperature-dependent period Period_1 are presented in thetemperature-independent period Period_2. The non-ideal coefficients ofthe temperature-dependent period Period_1 may be eliminated by dividingthe temperature-dependent period Period_1 by the temperature-independentperiod Period_2.

In an exemplary embodiment, the processor 112 evaluates temperature datax based on the temperature-dependent period Period_1 and thetemperature-independent period Period_2, and then evaluates atemperature value T based on the temperature data x. Because thenon-ideal coefficients of the temperature-dependent period Period_1 maybe eliminated by the temperature-independent period Period_2 (e.g., bydividing Period_1 by Period_1) during the evaluation of the temperaturedata x, the temperature value T evaluated from the temperature data x isreliable. The degradation of electronic components within the thermalsensor 102 (e.g., due to the aging effect or packaging stress does notaffect the accuracy of the thermal sensor 102. According to thehigh-accuracy temperature value T, the processor 112 can effectivelyoptimize the operations of the chip 100 (e.g., dynamic clock adjusting).The chip 100 with such a robust thermal sensor 102 works well inautomobile electronics, which guarantees the long service life ofautomobile electronics.

FIG. 2 depicts the details of the dual-phase voltage-to-frequencyconverter 108 in accordance with an exemplary embodiment of the presentinvention. The dual-phase voltage-to-frequency converter 108 includestwo selection circuits 202 and 204 and a switched-capacitor integratorloop 206. In the normal phase, the selection circuits 202 and 204 passthe temperature-dependent voltage VBE/2 and the temperature-independentreference voltage VREF to the switched-capacitor integrator loop 206 andthe switched-capacitor integrator loop 206 generates the oscillationsignal Sosc oscillating at the temperature-dependent frequency F1. Inthe coefficient capturing phase, the selection circuits 202 and 204 passdirect-current voltages VDD and VDD/2 to the switched-capacitorintegrator loop 206 and thereby the oscillation signal Sosc generated bythe switched-capacitor integrator loop 206 oscillates at thetemperature-independent frequency F1_Coeff.

The switched-capacitor integrator loop 206 comprises an integrator 208(including a switched-capacitor resistor 210), a voltage controlledoscillator (VCO) 212 and a divider 214. The switched-capacitor resistor210 is coupled to the integrator 208 through an input terminal of theintegrator 208. The switched-capacitor resistor 210 receives thetemperature-dependent voltage VBE/2 when the temperature-independentreference voltage VREF is coupled to a reference terminal of theintegrator 208, and receives the direct-current voltage VDD when thedirect-current voltage VDD/2 is coupled to the reference terminal of theintegrator 208. The voltage controlled oscillator 212 generates theoscillation signal Sosc according to an output voltage of the integrator208. The switched-capacitor resistor 210 mimics a resistor based on theoscillation signal after divider 214.

As shown, the switched-capacitor resistor 210 has two switches 216 and218 and a capacitor Cx. The switches 216 and 218 are controlled by anoutput signal and an inversed output signal of the divider 214,respectively. The capacitor Cx has a first terminal for receiving thetemperature-dependent voltage VBE/2 or the direct-current voltage VDDand a second terminal coupled to the input terminal of the integrator208 through the second switch 218. The switch 216 is coupled between thefirst terminal and the second terminal of the capacitor Cx.

According to the circuit design of FIG. 2, the temperature-dependentfrequency F1 and the temperature-independent frequency F1_Coeff bothinvolve information about the capacitor Cx of the switched-capacitorresistor 210 that might be affected by the aging effect or packagingstress. By combining the temperature-dependent frequency F1 and thetemperature-independent frequency F1_Coeff (e.g., dividing Period_1 byPeriod_2), non-ideal coefficients due to the capacitor Cx of theswitched-capacitor resistor 210 are eliminated. Temperature data xwithout non-ideal coefficients are evaluated. Thus, high-accuracytemperature value T is evaluated.

In the normal phase, the temperature-dependent frequency F1 correspondsto the temperature-dependent period Period_1, Rx·Cx(VBE/2VREF−1). Theremay be non-ideal variations on the capacitor Cx due to the aging effector packaging stress. To capture the present values of the capacitor Cx,the dual-phase voltage-to-frequency converter 108 is switched to thecoefficient capturing phase.

In the coefficient capturing phase, the temperature-independentfrequency F1_Coeff corresponds to the temperature-independent periodPeriod_2, Rx·Cx. The temperature-independent period Period_2 carries theinformation about the present values of the capacitor Cx.

The temperature-dependent frequency F1 and the temperature-independentfrequency F1_Coeff calculated by the frequency meter 110 and transmittedto the processor 112 may be converted to Period_1 and Period_2 by theprocessor 112. The processor 112 may further evaluate the temperaturedata x by the following calculation:

$x = {{\frac{{Period\_}1}{{Rx\_ cali} \cdot {Cx\_ cali} \cdot \left( {\frac{VBE\_ cali}{2{VREF\_ cali}} - 1} \right)} \cdot \frac{{Rx\_ cali} \cdot {Cx\_ cali}}{{Period\_}2}} = {{\frac{{Rx} \cdot {Cx} \cdot \left( {\frac{VBE}{2{VREF}} - 1} \right)}{{Rx\_ cali} \cdot {Cx\_ cali} \cdot \left( {\frac{VBE\_ cali}{2{VREF\_ cali}} - 1} \right)} \cdot \frac{{Rx\_ cali} \cdot {Cx\_ cali}}{{Rx} \cdot {Cx}}} = \frac{\left( {\frac{VBE}{2{VREF}} - 1} \right)}{\left( {\frac{VBE\_ cali}{2{VREF\_ cali}} - 1} \right)}}}$

Rx_cali, Cx_cali, VBE_cali and VREF_cali are constants measured infactory and burned in the chip 100. In the evaluated temperature data x,the non-ideal coefficient Rx·Cx are perfectly eliminated. The processor112 may evaluate the temperature value T by the following calculation:

T=ax+b

where a and b may be constants, a is a slope value, and b is an offsetvalue. From the high-accuracy temperature data x without non-idealcoefficients, the evaluated temperature value T is accurate. There maybe a considerable vibration on the capacitor Cx within theswitched-capacitor resistor 206 due to the aging effect or packagingstress. In the present invention, the non-ideal vibration on thecapacitor Cx does not affect the accuracy of the thermal sensor 102.

In some exemplary embodiments, the direct-current voltages passed to theswitched-capacitor integrator loop 206 are VDD and β·VDD. β is notlimited to ½, may be any constant.

In another exemplary embodiment, the temperature-independent referencevoltage VREF is not required. The disclosed dual-phasevoltage-to-frequency converter is coupled to a bandgap circuit in thenormal phase to perform a voltage-to-frequency conversion based on atemperature-dependent voltage generated by the bandgap circuit (withouttaking the temperature-independent reference voltage VREF intoconsideration). The disclosed dual-phase voltage-to-frequency converteris disconnected from the bandgap circuit in the coefficient capturingphase to perform the voltage-to-frequency conversion based on a singledirect-current voltage derived from the supply voltage VDD.

FIG. 3 is a flowchart depicting a thermal sensing procedure of thethermal sensor 102 in accordance with an exemplary embodiment of thepresent invention.

In step S302, the dual-phase voltage-to-frequency converter 108 isoperated in the normal phase to perform voltage-to-frequency conversionbased on the temperature-dependent voltage VBE/2 and thetemperature-independent reference voltage VREF and thereby generate anoscillation signal Sosc oscillating at the temperature-dependentfrequency F1.

In step S304, the frequency meter 110 calculates thetemperature-dependent frequency F1.

In step S306, the dual-phase voltage-to-frequency converter 108 isoperated in the coefficient capturing phase to performvoltage-to-frequency conversion based on two direct-current voltages VDDand VDD/2 and thereby the generated oscillation signal Sosc is switchedto oscillate at the temperature-independent frequency F1_Coeff thatincludes the information about of the non-ideal coefficients.

In step S308, the frequency meter 110 calculates thetemperature-independent frequency F1_Coeff.

In step S310, the processor 112 evaluates the temperature data x basedon the temperature-dependent frequency F1 (calculated from step S304)and temperature-independent F1_Coeff (calculated from step S308), andthen evaluates the temperature value T from the temperature data x(e.g., T=ax+b).

In some exemplary embodiments, the thermal sensor 102 may bemanufactured as a module to be equipped into any electronic device.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it should be understood that the invention isnot limited to the disclosed embodiments. On the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A thermal sensor, comprising: a bandgap circuit,outputting a temperature-dependent voltage; a dual-phasevoltage-to-frequency converter, coupled to the bandgap circuit in anormal phase to perform a voltage-to-frequency conversion based on thetemperature-dependent voltage, and disconnected from the bandgap circuitin a coefficient capturing phase to perform the voltage-to-frequencyconversion based on a supply voltage; and a frequency meter, coupled tothe dual-phase voltage-to-frequency converter to calculate atemperature-dependent frequency corresponding to the normal phase of thedual-phase voltage-to-frequency converter and a temperature-independentfrequency corresponding to the coefficient capturing phase of thedual-phase voltage-to-frequency converter, wherein thetemperature-dependent frequency and the temperature-independentfrequency are provided for temperature evaluation with non-idealcoefficient elimination.
 2. The thermal sensor as claimed in claim 1,further comprising: a charge pump circuit, pumping the supply voltage toa higher level for operations of the bandgap circuit, wherein thebandgap circuit further generates a temperature-independent referencevoltage to be coupled to the dual-phase voltage-to-frequency converterwith the temperature-dependent voltage.
 3. The thermal sensor as claimedin claim 2, wherein: the dual-phase voltage-to-frequency convertercomprises a switched-capacitor integrator loop; in the normal phase, thetemperature-dependent voltage and the temperature-independent referencevoltage are coupled to the switched-capacitor integrator loop and theswitched-capacitor integrator loop generates an oscillation signaloscillating at the temperature-dependent frequency; and in thecoefficient capturing phase, a first direct-current voltage and a seconddirect-current voltage derived from the supply voltage are coupled tothe switched-capacitor integrator loop and thereby the oscillationsignal generated by the switched-capacitor integrator loop oscillates atthe temperature-independent frequency.
 4. The thermal sensor as claimedin claim 3, wherein the switched-capacitor integrator loop comprises: anintegrator; a switched-capacitor resistor coupled to the integratorthrough an input terminal of the integrator, receiving thetemperature-dependent voltage when the temperature-independent referencevoltage is coupled to a reference terminal of the integrator, andreceiving the first direct-current voltage when the seconddirect-current voltage is coupled to the reference terminal of theintegrator; a voltage controlled oscillator, generating the oscillationsignal according to an output voltage of the integrator; and a divider,operating the switched-capacitor resistor to mimic a resistor based onthe oscillation signal.
 5. The thermal sensor as claimed in claim 4,wherein the switched-capacitor resistor comprises: a first switch and asecond switch, controlled by an output signal and an inversed outputsignal of the divider, respectively; and a capacitor, having a firstterminal for receiving the temperature-dependent voltage or the firstdirect-current voltage and a second terminal coupled to the inputterminal of the integrator through the second switch, wherein the firstswitch is coupled between the first terminal and the second terminal ofthe capacitor.
 6. The thermal sensor as claimed in claim 5, wherein: thetemperature-dependent frequency and the temperature-independentfrequency both involve information about the capacitor of theswitched-capacitor resistor that is affected by an aging effect orpackaging stress; and by combining the temperature-dependent frequencyand the temperature-independent frequency, non-ideal coefficients due tothe capacitor of the switched-capacitor resistor are eliminated andtemperature data for evaluation of a temperature value is evaluated. 7.The thermal sensor as claimed in claim 6, wherein the dual-phasevoltage-to-frequency converter further comprises: a first selectioncircuit, coupling the temperature-dependent voltage to the firstterminal of the capacitor of the switched-capacitor resistor in thenormal phase and coupling the first direct-current voltage to the firstterminal of the capacitor of the switched-capacitor resistor in thecoefficient capturing phase; and a second selection circuit, couplingthe temperature-independent reference voltage to the reference terminalof the integrator in the normal phase and coupling the seconddirect-current voltage to the reference terminal of the integrator inthe coefficient capturing phase.
 8. The thermal sensor as claimed inclaim 6, wherein the bandgap circuit comprises a bipolar junctiontransistor, and the temperature-dependent voltage is half of a voltagedifference between a base and an emitter of the bipolar junctiontransistor.
 9. The thermal sensor as claimed in claim 8, wherein: thesecond direct-current voltage is half of the first direct-currentvoltage.
 10. A chip, comprising: a thermal sensor as claimed in claim 1;and a processor, evaluating temperature data based on atemperature-dependent period derived from the temperature-dependentfrequency and a temperature-independent period derived from thetemperature-independent frequency, and evaluating a temperature valuebased on the temperature data, wherein when evaluating the temperaturedata, the processor eliminates non-ideal coefficients of thetemperature-dependent period by the temperature-independent period. 11.The chip as claimed in claim 10, wherein the thermal sensor furthercomprises: a charge pump circuit, pumping the supply voltage to a higherlevel for operations of the bandgap circuit, wherein the bandgap circuitfurther generates a temperature-independent reference voltage to becoupled to the dual-phase voltage-to-frequency converter with thetemperature-dependent voltage.
 12. The chip as claimed in claim 11,wherein: the dual-phase voltage-to-frequency converter comprises aswitched-capacitor integrator loop; in the normal phase, thetemperature-dependent voltage and the temperature-independent referencevoltage are coupled to the switched-capacitor integrator loop and theswitched-capacitor integrator loop generates an oscillation signaloscillating at the temperature-dependent frequency; and in thecoefficient capturing phase, a first direct-current voltage and a seconddirect-current voltage derived from the supply voltage are coupled tothe switched-capacitor integrator loop and thereby the oscillationsignal generated by the switched-capacitor integrator loop oscillates atthe temperature-independent frequency.
 13. The chip as claimed in claim12, wherein the switched-capacitor integrator loop comprises: anintegrator; a switched-capacitor resistor coupled to the integratorthrough an input terminal of the integrator, receiving thetemperature-dependent voltage when the temperature-independent referencevoltage is coupled to a reference terminal of the integrator, andreceiving the first direct-current voltage when the seconddirect-current voltage is coupled to the reference terminal of theintegrator; a voltage controlled oscillator, generating the oscillationsignal according to an output voltage of the integrator; and a divider,operating the switched-capacitor resistor to mimic a resistor based onthe oscillation signal.
 14. The chip as claimed in claim 13, wherein theswitched-capacitor resistor comprises: a first switch and a secondswitch, controlled by an output signal and an inversed output signal ofthe divider, respectively; and a capacitor, having a first terminal forreceiving the temperature-dependent voltage or the first direct-currentvoltage and a second terminal coupled to the input terminal of theintegrator through the second switch, wherein the first switch iscoupled between the first terminal and the second terminal of thecapacitor.
 15. The chip as claimed in claim 14, wherein: when evaluatingthe temperature data, the processor divides the temperature-dependentperiod by the temperature-independent period to eliminate the non-idealcoefficients which are contributed by the capacitor of theswitched-capacitor resistor that is affected by the aging effect orpackaging stress.
 16. The chip as claimed in claim 15, wherein: theprocessor evaluates the temperature value by performing the followingcalculation,T=ax+b, where T is the temperature value, x is the temperature data, ais a slope value, and b is an offset value.